Periodontal diseases are induced by communities of subgingival bacteria and result in destruction of supporting structures of the teeth. The diseases are diagnosed retrospectively by clinical parameters, however these parameters are poor indicators of ongoing disease activity or future attachment loss. An important research goal is to devise a means to identify sites in patients' mouths that are at risk of periodontal disease progression, thereby allowing site-specific preventive therapy. We hypothesize that active cell division of potential pathogens such as Porphyromonas gingivalis correlates with periodontal disease progression at specific sites. To test this hypothesis, a novel PCR-based molecular approach will be used to measure, in real time, the biosynthetic and growth activity of P. gingivalis cells in human subgingival plaque samples collected from healthy and disease sites. The project will test the hypothesis that P. gingivalis growth activity is greater in disease sites than in healthy sites of human subjects. The results will set the stage for future longitudinal studies that evaluate the efficacy of this approach, targeted to P. gingivalis as well as to other periodontal microorganisms, as clinically useful predictors of periodontal disease progression. Similar approaches also could be applied to other chronic, multifactorial diseases. When applied on a microbiomic scale, these methods could also significantly improve our understanding of specific microbiological activities within multi-species consortia including subgingival biofilms.